Minimally-invasive intracardiac ablation is the treatment of choice for various types of arrhythmias. To perform such treatment, the physician typically inserts a catheter through the vascular system into the heart, brings the distal end of the catheter into contact with myocardial tissue in areas of abnormal electrical activity, and then energizes one or more electrodes at or near the distal end in order to create tissue necrosis.
U.S. Patent Application Publication 2010/0030209, whose disclosure is incorporated herein by reference, describes a catheter with a perforated tip, which includes an insertion tube, having a distal end for insertion into a body of a subject. A distal tip is fixed to the distal end of the insertion tube and is coupled to apply energy to tissue inside the body. The distal tip has an outer surface with a plurality of perforations through the outer surface, which are distributed circumferentially and longitudinally over the distal tip. A lumen passes through the insertion tube and is coupled to deliver a fluid to the tissue via the perforations.
U.S. Pat. No. 5,957,961, whose disclosure is incorporated herein by reference, describes a catheter having a distal segment carrying at least one electrode extending along the segment and having a number of temperature sensors arranged along the distal segment adjacent the electrode, each providing an output indicative of temperature. The catheter is coupled to a power source, which provides radiofrequency (RF) energy to the electrode. Temperature processing circuitry is coupled to the temperature sensors and the power source, and controls power output from the power source as a function of the outputs of the temperature sensors.
U.S. Pat. No. 6,312,425, whose disclosure is incorporated herein by reference, describes an RF ablation catheter tip electrode with multiple thermal sensors. A tip thermal sensor is located at or near the apex of the distal-end region, and one or more side thermal sensors are located near the surface of the proximal-end region. The electrode is preferably an assembly formed from a hollow dome-shaped shell with a core disposed within the shell. The side thermal sensor wires are electrically connected inside the shell and the core has a longitudinal channel for the side thermal sensor wires welded to the shell. The shell also preferably has a pocket in the apex of the shell, and the end thermal sensor wires pass through the core to the apex of the shell.
U.S. Pat. No. 6,217,574, whose disclosure is incorporated herein by reference, describes an irrigated split tip electrode catheter. A signal processor activates an RF generator to transmit a low level RF current to each electrode member of the split tip electrode. The signal processor receives signals indicative of the impedance between each electrode member and one or more surface indifferent electrodes and determines which electrode members are associated with the highest impedance. Such electrode members are stated to be those in greatest contact with the myocardium.
U.S. Pat. No. 6,391,024, whose disclosure is incorporated herein by reference, describes a method of assessing the adequacy of contact between an ablation electrode and biological tissue. The method measures the impedance between an ablation electrode and a reference electrode at a first and second frequencies. A percentage difference between the first-frequency impedance and the second-frequency impedance is stated to provide an indication of the state of electrode/tissue contact.
U.S. Pat. No. 6,730,077, whose disclosure is incorporated herein by reference, describes a cryocatheter for treatment of tissue. A signal conductor extends through the catheter to the catheter tip and connects to a thermally and electrically conductive shell or cap that applies an RF current to the region of tissue contacted by the tip. A tissue impedance path between the signal lead and a surface electrode mounted on the patient's skin is monitored to develop a quantitative measure of tissue contact at the distal tip.
U.S. Patent Application Publication 2014/0171936 to Govari, which is incorporated herein by reference, describes apparatus that includes an insertion tube having a distal end configured for insertion into proximity with tissue in a body of a patient and containing a lumen having an electrical conductor for conveying electrical energy to the tissue. The apparatus further includes a conductive cap attached to the distal end of the insertion tube and coupled electrically to the electrical conductor, wherein the conductive cap has an outer surface. In addition there are a multiplicity of optical fibers contained within the insertion tube, each fiber terminating in proximity to the outer surface of the cap, and being configured to convey optical radiation to and from the tissue while the electrical energy is being conveyed to the tissue.